Warming up to weird weather

As Chicago finally heats up, some experts point to altered jet stream and effects of climate change

August 22, 2013|By Pete Reinwald, Chicago Tribune reporter

Summer as Chicago knows it made only a brief appearance in mid-July, when there was a stretch of 90-degree days — the last on July 19. Eight days later, in the middle of beach season, the high was 65. “I do think it’s kind of weird. ... You’re seeing mid-90s for three days in the middle of July and then you’re wearing sweaters,” said Paul Pastelok, senior meteorologist and lead long-range forecaster at AccuWeather. (Chris Sweda, Chicago Tribune)

In a year wrapped in weird weather, the past few weeks have been nearly perfect. Which is weird.

Chicago on Wednesday hit 90 degrees for the first time in more than a month. Which for July and August is weird.

"Summer's trying to redeem itself at the eleventh hour," Logan Square resident Jill Shtulman said Wednesday with a laugh. "Normally the summers around here should begin on Memorial Day, and it's beginning on Labor Day instead. There's a little disconnect there."

Chicago started the year in the midst of a record stretch of 335 days without an inch or more of snow. Then we had the wettest April on record. Cold and wet weather in spring and early summer flooded homes, postponed baseball games and disrupted concerts and barbecues. July brought warm and dry weather, with exceptions — particularly one day late in the month when we exchanged T-shirts for sweatshirts. Then August started cooler than normal, with a hint last week of autumn.

"Worst. Summer. Ever," Shtulman wrote early this month in an email.

And maybe the weirdest too? What's going on here?

Weather experts say a warming planet has led to changed atmospheric circulation patterns in the jet stream, the fast-moving river of air that separates cold air from warm air and dictates weather patterns across the globe. They say the features within the jet stream that bring clouds and precipitation or dryness and extreme temperatures — low-pressure troughs and high-pressure ridges — are changing their movement and duration, creating unusual weather patterns that lock in place and cause major floods, cold spells and heat waves.

Consider McGrath, Alaska.

The town in May set 10 temperature records — six for daily lows around the middle of the month and four for daily highs near the end of the month, reported Anchorage television station KTVA.

Then, on June 17, McGrath hit an all-time record of 94 degrees.

Now consider Chicago.

Summer as we know it showed up briefly in mid-July, with a stretch of temperatures in the 90s, the last of them July 19. Eight days later we managed a high of only 65 degrees — a record low for a high temperature for that date. McGrath, Alaska — almost 4,000 miles to the northwest — hit 85 degrees on that day, according to Weather Underground, owned by The Weather Channel.

"I do think it's kind of weird, weird in the fact that we've seen these ups and downs that are extreme," said Paul Pastelok, senior meteorologist and lead long-range forecaster at AccuWeather. "You're seeing mid-90s for three days in the middle of July and then you're wearing sweaters."

Experts say our weather could be linked to extreme conditions this summer around the globe, including cold and rain in Atlanta and record-breaking heat in the western U.S., eastern China and central Europe.

Some meteorologists attribute the weird weather to vacillations that have played out throughout history.

"The weather seems to be doing what it always does," said Mike Tannura of T-storm Weather, a Chicago-based weather-forecasting service that focuses on agricultural commodities. "It fluctuates."

This Chicago summer differs sharply from last summer, whose frequent 90-degree temperatures sapped ponds and marshes and devastated crops statewide and beyond. Yet meteorologists point out that Chicago temperatures this summer, though about 5 degrees cooler than last summer's, run close to average.

"But that doesn't tell the whole story," Stu Ostro, senior meteorologist at The Weather Channel, wrote in an email. "The (average) isn't extreme, but a day in late July with an afternoon high temp of 65 degrees is."

Ostro counts himself among scientists who subscribe to the theory of global warming and that humans are increasing the planet's temperature largely through the burning of fossil fuels, which emit carbon dioxide.

The National Aeronautics and Space Administration says Earth's average temperature has risen 1.4 degrees over the past century, and the U.S. Environmental Protection Agency says increased destructive weather has accompanied the rising temperature. Scientists say the temperature increase correlates with an increase in greenhouse gases, including carbon dioxide and water vapor, in the atmosphere.

"I'm in the camp with Stu Ostro," WGN chief meteorologist Tom Skilling said. "He was a denier. He started keeping track of all the anomalies. You just had to reach the point where you had to say to yourself, 'Something's going on here.'"

The global warming theory continues to spur intense political and cultural debate, including whether Earth is embarking on climate change through natural cycles like those of the sun and whether global warming is a hoax created to enrich its proponents, including green companies and producers of biofuels.